SEC Schedule III Rollforward of Real Estate Assets and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Real estate at Cost	$ 16,703,757	$ 16,454,967	$ 16,344,244
Real Estate Other Acquisitions	514,950	33,481	347,345
Real Estate Improvements	1,615,077	315,762	324,114
Real Estate Cost Of Real Estate Sold	338,425	100,453	560,736
Real estate at Cost	18,495,359	16,703,757	16,454,967
Reconciliation Of Real Estate Accumulated Depreciation Roll Forward
Real Estate Investment Property, Accumulated Depreciation	2,894,374	2,530,945	2,228,425
Real Estate Accumulated Depreciation Depreciation Expense	427,189	452,793	428,788
Real Estate Accumulated Depreciation Real Estate Sold	224,489	89,364	126,268
Real Estate Investment Property, Accumulated Depreciation	$ 3,097,074	$ 2,894,374	$ 2,530,945